Within-brood Variation Research Articles

Effects of a novel ectoparasite on condition and mouth coloration of nestling barn swallows

Abstract Parasites have profound and widespread implications for the ecology and evolution of hosts, and human activity has increased the frequency of interactions between hosts and parasites that have not co-evolved. For example, by building habitat attractive for nesting, humans might have facilitated range expansion by cliff swallows (Petrochelidon pyrrhonata) and barn swallows (Hirundo rustica) in North America, concurrently allowing a haematophagous ectoparasite of cliff swallows, the swallow bug (Oeciacus vicarious), to infest the nests of barn swallows. We found that in barn swallow nests infested with swallow bugs, nestlings weighed less and had lower haematocrit, and the within-brood variation in body mass and tarsus length was higher. Information about these negative effects might be available to parents via mouth coloration, a condition-dependent component of the begging signal. We found that nestlings from infested broods had lower-intensity carotenoid-based and ultraviolet mouth colours, although most elements of colour were unrelated to parasites. Host switching by the swallow bug offers excellent opportunities to understand the direct and indirect effects of a novel parasite and might also afford insights into how parasites cope with selective pressures exerted by closely related hosts with key ecological differences.

Adaptive and Plastic Responses to Environmental Variation: Introduction to a Virtual Symposium in The Biological Bulletin.

Adaptive and Plastic Responses to Environmental Variation: Introduction to a Virtual Symposium in The Biological Bulletin.

Supplementary feeding increases nestling feather corticosterone early in the breeding season in house sparrows.

Several studies on birds have proposed that a lack of invertebrate prey in urbanized areas could be the main cause for generally lower levels of breeding success compared to rural habitats. Previous work on house sparrows Passer domesticus found that supplemental feeding in urbanized areas increased breeding success but did not contribute to population growth. Here, we hypothesize that supplementary feeding allows house sparrows to achieve higher breeding success but at the cost of lower nestling quality. As abundant food supplies may permit both high‐ and low‐quality nestlings to survive, we also predict that within‐brood variation in proxies of nestling quality would be larger for supplemental food broods than for unfed broods. As proxies of nestling quality, we considered feather corticosterone (CORT f), body condition (scaled mass index, SMI), and tarsus‐based fluctuating asymmetry (FA). Our hypothesis was only partially supported as we did not find an overall effect of food supplementation on FA or SMI. Rather, food supplementation affected nestling phenotype only early in the breeding season in terms of elevated CORT f levels and a tendency for more variable within‐brood CORT f and FA. Early food supplemented nests therefore seemed to include at least some nestlings that faced increased stressors during development, possibly due to harsher environmental (e.g., related to food and temperature) conditions early in the breeding season that would increase sibling competition, especially in larger broods. The fact that CORT f was positively, rather than inversely, related to nestling SMI further suggests that factors influencing CORT f and SMI are likely operating over different periods or, alternatively, that nestlings in good nutritional condition also invest in high‐quality feathers.

The transition from dependence to independence in birds

Avian parents initially provide their offspring with resources such as food and protection from predators but the offspring then undergo a period of transition from dependency to independence. That transition represents a crucial period of an individual’s life as their inexperience in simultaneously searching for food and avoiding predators’ means that the risks of mortality are higher than during other periods of their life. Unfortunately, our understanding of the transition to independence has lagged behind other life history stages due to the logistical challenges associated with tracking individuals after they have left the relatively safe confines of the nest. However, recent technological advances that have enabled individuals to be tracked remotely have dramatically increased our understanding of the process by which offspring acquire independence. First, interspecific studies of birds have demonstrated that the offspring of species that suffer both high levels of nest predation and ectoparasite-induced nestling mortality leave the nest comparatively sooner than the offspring of species that suffer lower levels of nest predation and ectoparasite-induced nestling mortality. Second, intraspecific studies have become much more prevalent in recent years as new technologies have been used to show that between-brood or litter variation in the timing of independence is influenced by predation risk, ectoparasite-induced nestling mortality and parent-offspring conflict over the provision of care. Further studies have shown that within-brood variation in the timing of independence also occurs as a result of both genetic effects such as parentage and offspring sex, and parental effects such as hatching asynchrony, that result in inequalities between siblings. In summary, there is considerable variation in the process by which avian offspring acquire independence at the interspecific and intraspecific levels. However, whilst we have a reasonable understanding of the causes of such variation, our understanding of the consequences of such variation is less developed and deserves further research.

Fatty Acids of Densely Packed Embryos ofCarcinus maenasReveal Homogeneous Maternal Provisioning and No Within-Brood Variation at Hatching

Embryonic development of decapod crustaceans relies on yolk reserves supplied to offspring through maternal provisioning. Unequal partitioning of nutritional reserves during oogenesis, as well as fluctuating environmental conditions during incubation, can be sources of within-brood variability. Ultimately, this potential variability may promote the occurrence of newly hatched larvae with differing yolk reserves and an unequal ability to endure starvation and/or suboptimal feeding during their early pelagic life. The present study evaluated maternal provisioning by analyzing fatty acid (FA) profiles in newly extruded embryos of Carcinus maenas Also assessed were the dynamics of such provisioning during embryogenesis, such as embryo location within the regions of the brooding chamber (left external, left internal, right external, and right internal). The FA profiles surveyed revealed a uniform transfer of maternal reserves from the female to the entire mass of embryos, and homogeneous embryonic development within the brooding chamber. Although C. maenas produces a densely packed mass of embryos that are unevenly distributed within its brooding chamber, this factor is not a source of within-brood variability during incubation. This finding contrasts with data already recorded for larger-sized brachyuran crabs, and suggests that the maternal behavior of C. maenas promotes homogeneous lipid catabolism during embryogenesis.

Nestling sex and plumage color predict food allocation by barn swallow parents

Despite parents are equally related to all of their progeny, they may differentially invest in offspring that provide the highest fitness return. Sons and daughters can differ in reproductive value, especially in species where fitness is predicted by the expression of sexually selected traits. In many birds, offspring plumage coloration functions as a honest signal of individual quality, thus allowing parents to differentially invest in offspring of either sex accordingly. Here, we tested whether parents allocate different amounts of food depending on plumage color of their male and female offspring. As a model, we used the barn swallow (Hirundo rustica), a species where large among- and within-brood variation in ventral plumage color exists and male reproductive success varies according to ventral plumage coloration. We recorded the proportion of feedings obtained and body mass variation by dyads of same-sex and similar-sized nestlings subjected to either experimental darkening of their ventral plumage color or to a sham treatment. Plumage darkening enhanced food provisioning and body mass gain of males but not of females. Because darker ventral coloration is associated with larger reproductive success in male barn swallows, these results suggest that parents tune their effort toward more valuable male offspring that are likely to provide the greatest fitness returns. Our study thus suggests that parents are selected to differentially invest in offspring of either sex according to a trait expressed in early life, which is relevant to intrasexual competition for access to mates at sexual maturity.

Temperature Effects on Reproductive Allocation in the Sandhopper Talorchestia capensis.

In invertebrates, environmental temperature may induce mothers to invest differently in the early development of their offspring. In ectotherms, temperature affects offspring phenotype so that colder mothers produce larger eggs. However, developmental mode and maternal size also contribute to the determination of optimal offspring size. When the maternal experience closely matches the offspring's probable future conditions (e.g., direct developers), it is expected that mothers will produce eggs of similar size within the same brood. While temperature directly affects the size of the eggs (temperature size rule), with potential indirect links to egg number (trade-off between egg size/number), maternal size can be a limiting factor in determining the optimal number of eggs, especially if eggs are brooded. We evaluated the role of temperature in shaping early ontogeny in the sandhopper Talorchestia capensis (Crustacea: Amphipoda), investigating within-brood and among-female variation in the size of the eggs. To test for causal relationships among temperature, maternal size, egg size and number, we used an information theoretic approach combined with path analysis. Sandhoppers invested in smaller eggs at higher temperatures, with no significant within-brood variation in the size of the eggs. Regardless of temperature, we found significantly different investment in egg size among females. Path analyses showed a simultaneous contribution of temperature and maternal size to the optimal size and number of eggs within a single clutch. Strong inter-individual variability in maternal investment could generate phenotypic variation within a population and promote population fitness.

Physiological development of brooded larvae from two pocilloporid corals in Taiwan

In southern Taiwan, brooded larvae of Pocillopora damicornis and Seriatopora caliendrum are released year-round in synchrony with new moons, and each larval release occurs over multiple days. Using P. damicornis and S. caliendrum as a model system, we describe within-brood variation in larval phenotypes and test for release-day effects that influence larval performance in the pelagic phase. Research was conducted in 2010 using larvae from corals collected in June and July from Nanwan Bay (21°56.179′N, 120°44.85′E). In June, larval phenotypes of both species were characterized immediately following release, and their competency to settle assessed. In July, larvae of P. damicornis were collected on 3 days over the peak release period and incubated for 7–11 days at 28.0 °C and 320 μmol quanta m−2 s−1; their phenotypes and settlement competency were measured every 2 days. P. damicornis larvae released close to peak release were 1.6 times larger in size, contained twice the number of Symbiodinium larva−1, and were 44 % more likely to settle in the first 24 h than larvae released early in the brood. In addition, peak-release larvae respired at a lower rate than larvae released late in the brood. Similarly, S. caliendrum larvae released close to peak release were 1.4 times larger in size and were 33 % more likely to settle in the first 5 h than larvae released early in the brood. In July, P. damicornis larvae differed between early (2 days prior to peak), peak, and late (2 days after peak) release. Protein content of early-release larvae was lower than peak- and late-release larvae, and this difference persisted throughout the development. Further, release day affected the way larval respiration varied throughout development. By showing that brooded coral larvae differ between release days and display maternal effects influencing performance in the swimming phase, our results suggest that pocilloporid corals utilize bet-hedging to increase reproductive success.

Inter-individual and within-brood variability in the fatty acid profiles of Norway lobster, Nephrops norvegicus (L.) embryos

The present study investigated the existence of inter-individual and within-brood variability in the fatty acid (FA) profile of developing embryos of Nephrops norvegicus. In all surveyed females (n = 5), the quantitatively most important FAs were as follows: 22:6n-3 (20.8 ± 3.9% average of total FA ± standard error), 18:1n-9 (19.5 ± 2.0%), 16:0 (15.2 ± 3.4%), 20:5n-3 (10.2 ± 1.4%), 16:1n-7 (8.9 ± 1.6%), and 18:1n-7 (5.7 ± 1.3%). Differences in FA profiles of embryos in the same clutch were assessed using brooding chamber side (left and right) and pleopod (1st and 2nd, 3rd and 4th, and 5th) as predictive factors. There were no significant differences in the FA composition of embryos sampled from both sides of the brooding chamber in 4 of the 5 surveyed females. However, all females exhibited significant differences in the FA profiles of embryos sampled from different pleopods. Both saturated FA (SFA) and highly unsaturated FA (HUFA) present in developing embryos exhibited marked differences along the breeding chamber. Overall, FA reserves appeared to vary significantly within broods, which can ultimately be reflected on early larval survival. A potential cause for the within-brood variation recorded in the FA profile of developing embryos include (1) differential female investment during ovarian maturation, mainly due to variation in food quality/availability; (2) differential lipid catabolism during the incubation period of developing embryos, as a consequence of embryos position within the female’s brooding chamber; or (3) differential female investment during ovarian maturation amplified by differential lipid catabolism during the incubation period.

Competition for resources modulates cell-mediated immunity and stress hormone level in nestling collared doves ( Streptopelia decaocto)

Competitive stress imposed by hatching asynchrony may affect developmental trajectories of offsprings by regulating resource allocation between growth and other fitness-related traits. For instance, the down-regulation of immunity is a commonly observed phenomenon under stressful conditions. However, physiological mechanisms that regulate resources allocation to growth and immune functions in response to competition for resources, as well as inter-sexual differences in physiological strategies, are still poorly investigated. To partially fill this gap, we first conducted a descriptive study on chicks of the collared dove ( Streptopelia decaocto), a species producing two chicks per brood. Our results show that first hatchlings (seniors) were bigger, showed lower baseline corticosterone levels (CORT) and showed a higher cell-mediated immunoresponsiveness (CMI) than late hatchlings (juniors). However, when controlling for body size, only CMI remained weaker in junior chicks suggesting differences in strategies of resource allocation between siblings. Interestingly, CORT in juniors increased with increasing within-brood hierarchy. But, while within-brood variation in CMI followed the opposite pattern of variation in CORT, we found no evidence that inter-individual variation in CMI was directly related to CORT. In addition hatching-rank related differences in body size, CMI and CORT was similar between sexes. To ensure that the lower phenotypic value expressed by juniors was not fully related to a lower quality of the late-laid egg, we experimentally suppressed the competitive stress experienced by juniors by removing the first-laid egg (i.e. the egg normally producing a senior chick). In the absence of their brood mates, juniors were bigger, had lower levels of CORT and showed a higher CMI than juniors raised in two-brood chicks, suggesting that body size, CMI and CORT in juniors were modulated by the competitive stress. Overall, this study suggests that juniors respond to within-brood competition by elevating CORT and down-regulating CMI. In this context, the role of CORT, as a mechanism regulating physiological strategies related to growth and immunocompetence is discussed.

Blood parameters as consistent predictors of nestling performance in great tits ( Parus major) in the wild

Fourteen blood profile variables were analysed in 12-day-old nestlings of great tits ( Parus major) in the wild. Except for plateletocrit and platelet distribution width, the traits showed a consistent pattern of variation, with significant intra-brood repeatabilities; they were shown to be significant predictors of nestling performance as measured by survival from hatching to fledging. It is concluded that all blood characteristics that show consistent within-brood variation may be useful as indicators of some aspects of nestling condition/health status in wild birds.

Effects of maternal and embryo characteristics on post-fertilization provisioning in fishes of the genus Gambusia

Maternal provisioning of embryos in Gambusia (Poeciliidae) entails both production of large, yolky eggs and mother-to-embryo transfer of nutrients, the latter of which is readily quantified using injection of radiolabeled nutrients. We assayed patterns of nutrient transfer in broods of 26 Gambusia geiseri and 23 Gambusia affinis females, using injection of tritiated leucine. We examined maternal and embryo characteristics affecting the instantaneous rate of transfer and characterized the pattern of transfer to individual embryos within broods. Maternal (female size and condition) and brood characteristics (mean embryo size, developmental stage, brood size) did not predict the mean level of nutrient transfer to embryos in a brood for either species. Within broods, individual provisioning of embryos was not related to developmental stage, but was related to embryo mass in G. affinis with nutrient transfer higher to larger embryos. In addition, overall within-brood variation in nutrient transfer, measured as coefficient of variation in embryo radioactivity, was higher in G. affinis than in G. geiseri.

Increase in a heat-shock protein from blood cells in response of nestling house martins (Delichon urbica) to parasitism: an experimental approach.

Heat-shock proteins (HSPs) are synthesized by animals and plants in response to various stressors. The level of the HSP60 stress protein was measured from the cell fraction of peripheral blood obtained from nestling house martins (Delichon urbica) to test whether ectoparasitism increased the concentration of stress protein. We assessed HSP from nestlings raised in nests previously treated with an insecticide or infested with 50 martin bugs (Oeciacus hirundinis). In addition, haematozoa infections were checked in blood smears. Nestlings from parasite-infested nests, or nestlings infected with trypanosomes, had increased levels of HSP in their blood cells. Nestling growth as determined from wing length was negatively related to HSP60 levels and within-brood variation in wing length increased with increasing levels of the stress protein independently of treatment and infection by trypanosomes. These results suggest HSPs may play a role in host-parasite interactions, and that they can be used reliably for measuring physiological responses to parasites.

Heritability of nestling growth in cross-fostered European Starlings Sturnus vulgaris.

In altricial birds, growth rates and nestling morphology vary between broods. For natural selection to produce evolutionary change in these variables, ther must exist heritable variation. Since nestling traits are not any longer presents in parents, traditional offspring-parent regressions cannot estimate heritabilities of these. In this study, a partial cross-fostering experiment was performed, where nestlings of the European Starling (Sturnus vulgaris) were reciprocally exchanged between nests. The experiment demonstrated a significant heritability of nestling tarsus length and body mass, but not of the growth trajectories followed by individual nestlings. the heritability estimate for tarsus length obtained in the cross-fostering experiment using full-sib analysis was lower than those obtained by offspring-parent regressions. This is likely due to a genotype-by-environment effect on tarsus length, with nestlings destined to become large but in poor condition having a low probability of appearing as parents. The main reason for the low heritability of growth was probably the large within-brood variation in growth pattern due to the initial size hierarchy of nestlings. Nestlings demonstrated targeted growth, where small-sized nestlings that initially grew slower than their siblings, managed to catch up.

Variation in Body Mass of Wild Canvasback and Redhead Ducklings

We assessed variation in body mass of ducklings in single- and mixed-species broods of wild Canvasbacks (Aythya valisineria) and Redheads (Aythya americana) 20-50 days old. Body mass of canvasback ducklings was not affected by year and season (early vs. late hatch date) despite changes in water conditions. Mean body mass of male and female Canvasbacks did not differ in Class IIA but did differ in older age classes. Within-brood differences in body mass tended to be higher in Class IIA ducklings (6-7% of mean body mass for Canvasbacks, 9-11% in Redheads) and generally declined to 4-6% in Class IIC and older ducklings. Some within-brood differences were as high as 20-30% of mean body mass. Tests to assess sources of within-brood variation (age, sex, and season) in body mass for Canvasbacks were inconclusive. Variation within broods was generally less than that among broods for both Canvasbacks and Redheads. The lack of differences in duckling body mass between single- and mixed-species broods for any age class, sex, or species suggests that mass was not affected by interspecific brood parasitism.

An experimental study of brood division in white-throated sparrows

Parental care towards experimentally restrained white-throated sparrow, Zonotrichia albicollis, fledglings was examined for evidence of brood division. Brood division occurred in 14 of 17 broods and was characterized by distinct but overlapping preferences by parents for particular brood members. The combined efforts of the parents usually resulted in an even distribution of resources among the brood. However, in some cases, brood division caused some fledglings to receive more food than others. Within-brood variation in food received was correlated with the difference between parents in parental effort. Brood division was maintained by the location of the young for some parents and by the identity of the young for other parents. It is suggested that changes in brood mobility might necessitate a shift in the cues used to discriminate between fledglings in order for parents to maintain brood division through the post-fledging period.